Add a Clock and TickClock interface for mocking out time

base/time/default_tick_clock.h

Index: base/time/default_tick_clock.h
diff --git a/base/time/default_tick_clock.h b/base/time/default_tick_clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..553a8d28e8e3339b7ce50df4f67c0af4b05bd333
--- /dev/null
+++ b/base/time/default_tick_clock.h
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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_DEFAULT_TICK_CLOCK_H_
+#define BASE_DEFAULT_TICK_CLOCK_H_
+
+#include "base/base_export.h"
+#include "base/compiler_specific.h"
+#include "base/time/tick_clock.h"
+
+namespace base {
+
+// DefaultClock is a Clock implementation that uses TimeTicks::Now().
+class BASE_EXPORT DefaultTickClock : public TickClock {
+ public:
+  virtual ~DefaultTickClock();
+
+  // Simply returns TimeTicks::Now().
+  virtual TimeTicks NowTicks() OVERRIDE;
+};
+
+}  // namespace base
+
+#endif  // BASE_DEFAULT_CLOCK_H_